Morphology, morphometry and some aspects of clinical anatomy in the skull and mandible of Sharri sheep

The aim of this study was to investigate and record data on the morphometrical parameters of the skull and mandible in Sharri sheep. We have evaluated 34 skulls (24 females and 10 males) of Sharri sheep (Ovis aries), a local breed of sheep from Northern Macedonia. Fifty-one measurements were evaluated in total: 37 parameters on the skull and 14 parameters on the mandible. The results of the study show that, in general, the morphology and morphometric parameters of the skull and mandible, of Sharri sheep are similar to those of other sheep breeds with few differences. The mean skull length (SL), skull height (SH), distance between two supraorbital foramina (DBTSF), orbital length (OL), mandible length (ML) and Sharri sheep diastema (D) were 247.47 ± 13.12 mm, 104.71 ± 6.21 mm, 50.73 ± 3.44 mm, 41.21 ± 1.99 mm, 185.91 ± 13.33 mm and 45.81 ± 3.73 mm, respectively. The results also show that out of 51 parameters, only 13 show a statistically significant difference between females and males, particularly the distance of akrokranion to opisthion (AO), articular surface length of mandibular condyle (ASL) and anterior limit of the mandibular foramen to cranial border of ramus mandible (RBMFRMRM). The findings of this study are important in many aspects: morphologically, morphometrically and especially clinically, during surgical interventions in the head region. With a lack of information in current literature on the investigated parameters in this sheep breed, the present data are a solid basis for further studies in comparative anatomy with other ruminants and in other areas such as zooarchaeology and animal welfare.


Introduction
Sharri or Sharplaninska pramenka sheep are a local breed of sheep (Ovis aries Linnaeus, 1758) found in Northern Macedonia, and they represent almost 30% of the total sheep population in this country. Sharri sheep are a unicolor, white breed with a long tail and triple production (milk-meat-wool) (Dzabirski et al. 2013). This strain has the advantages of natural hardiness, grazing abilities, and are well adapted to a cold mountain climate, since this breed lives near the Sharri mountains. The rams are horned and reach about 44-45 kg, and ewes are polled and reach about 30-32 kg (Kugler 2009;Dzabirski et al. 2013;Bytyqi et al. 2014).
The structure of the skull is a unique feature of each animal, allowing for the distinguishment of not only species and breeds, but also individuals. Sexual dimorphism is strongly manifested in the skeleton of the head of ruminants (Kobryńczuk et al. 2008b). The results of many studies made on these bones are a great contribution in areas of taxonomy, comparative anatomy (Özcan et al. 2010;Karimi et al. 2011;Mohamed et al. 2016;Dalga et al. 2018) and in the clinical veterinary practice, surgery, implantology, stereotaxic practices, animal welfare, etc. (Dalga, and Aslan 2020;Wehausen and Ramey 2000). Current morphometric study results can be used to determine the type of bone obtained in excavation studies. Assumptions can then be made about the history of the excavation area, as well as the livestock conditions of that time. This is done with morphological determinations using morphometric results (Onar et al. 2015). In addition, differences between the sexes were found on the skull and mandible. With these differences, gender analysis can be made by looking at the measurement points (Marzban et al. 2018;Gündemir et al., 2020).
The skeleton of the head consists of two parts. The first part surrounding the brain -neurocranium and the second part surrounding the oral and nasal cavities -splanchnocranium are composed by different paired and unpaired bones (König and Liebich 2020;N. A. V. 2017). Mandibles provide support for lower incisive teeth, premolars, molars, and the entire base structures of the mouth.
Sheep under natural conditions often suffer from problems such as: abscesses in the jaw, damage to and loss of teeth, fractures of the mandible, temporomandibular joint damages etc. In these conditions, preventive or even surgical interventions are necessary. The success of which depends on a very good knowledge of clinical anatomy of the mandible, including: mental and mandibular foramina which have a fundamental importance in regional anesthesia.
No anatomical studies have been carried out so far in Sharri sheep. With this study, we aim to show and record morphological, morphometric and clinically relevant data for the skull of this breed, the number of which is heading towards the limit of extinction.

Material and methods
Skulls and mandibles of 24 females and 10 male adult Sharri sheep were used in this study. The research material was collected from Northern Macedonia and approved by the Ethics committee of University of Tetovo,.
The skulls of the sheep were obtained after slaughter. Bones were cleaned by standard procedures after the skin and soft tissue were removed. Measurements were made based on the instructions of von den Driesch (1976) in own modification. In this study we have measured 51 parameters in total: 37 parameters on the skull and 14 on the mandible. Also, we have evaluated five indices of the skull. All measurements were taken in millimeters with a digital caliper (± 0.2 mm). The photographs of the samples were made with a Samsung photo camera NX210 20.3 MP.

Skull measurements (Figs. 1, 2, 3 and 4)
1. Skull length (SL) -max. length of the skull from the rostral tip of the incisive bones (Prosthion) to the external occipital protuberance 2. Cranial length (CL)-distance from the nuchal crest to the junction of the left and right nasofrontal sutures on the median plane 3. Max. width of neurocranium (MWNC)-distance from the most lateral point of the cranial cavity on the left to the most lateral point of the cranial cavity on the right 4. Facial length (FL)-distance from the junction of the left and right nasofrontal sutures in the median plane to the rostral tip of the incisive bones (Prosthion) 5. Facial width (FW) -distance between the caudal extents of the orbital margin (Ectorbital -Ectorbital) 6. Entorbitale-Entorbitale (EE)-the width between the rostral borders of the orbits 7. Length of the interfrontal suture (LIFS) 8. Bregma to Akrokranion (BA)-distance from parietofrontal suture to nuchal line 9. Greatest length of nasal bone (GLNB) 10. Incisive bone to nasal bone (IBNB)-distance from the rostral tip of the incisive bones (Prosthion) to the tip of septal process 11. Prefacial width (PFW) -the distance between two facial tuberosities 12. Distance between two supraorbital foramina (DBTSF) 13. Skull height (SH)-from the level of the highest point of the frontal bone to the tip of the paracondylar process 14. Greatest length of the lacrimal bone (GLLB) 15. Greatest length of the zygomatic bone (GLZB) 16. Distance from Prosthion to PM1 (PPM1) -the distance between the rostral tip of incisive bones to first premolar tooth 17. Dental length (DL)-distance from the rostral tip of incisive bones (Prosthion) to caudal border of the third molar tooth 18. Cornual process length (CPL)-the distance from the base to the tip of the cornual process 19. Cornual process width (CPW)-the transverse width of the proximal part of the cornual process 20. Infraorbital foramen to alveolar margin (IFAM) to the highest point of the condylar process 4. Mandibular notch to coronoid process (MICP)-the distance from the mandibular notch to the highest point of the coronoid process 5. M3 to mandibular angle (M3MA)-the distance from third molar tooth to the angle of the mandible 6. Articular surface length (ASL) -the length of the articular surface of the condylar process 7. First incisor tooth to mandibular angle (FITMA)-the distance from the first incisive tooth to the angle of the mandible 8. First incisor tooth to first premolar (FITFPm) -the distance between first incisor to the first premolar tooth 9. Lateral alveolar root to mental foramen (LARMF)shortest distance from the mental foramen to the lateral extent of the corner incisor alveolus 10. Diastema (D)-from caudal border of the corner incisor alveolus to rostral border of first premolar alveolus 11. Lower molar row from PM1 to M3 (LMR)-the length between first premolar tooth and third molar tooth of the mandible 12. Rostral border of the mandibular foramen to rostral margin of ramus mandible (RBMFRMRM) -the distance between the rostral limit of the mandibular foramen to the rostral margin of the ramus of mandible

Statical analysis
Means and standard deviations of all measurements were calculated for both males and females. Independent t-test was used to reveal the differences between genders. P values are given in the results tables. The correlations between the measurements examined in the study were examined by using Pearson correlation coefficients. SPSS (version 22) software package was used for the statistical analysis.

Morphometrics
The results and statistical differences of the skull measurements are shown in Tables 1 and 2. According to these results, the differences between males and females in BA, IBNB, SH, FMW, AO and IBPCW were statistically significant. The most important difference was in AO. Male measurement values for AO were higher than that of females. SL and SW values were higher for females, while SH values were higher for males. However, the difference between these values was statistically insignificant. The parameters of foramen magnum in females were bigger than in male individuals and only the difference in foramen magnum width (FMW) was found to be statistically significant.
A correlation test was used with skull measurements. The strongest correlations were observed between the individual longitudinal dimensions of the skull. However, a correlation value between the FL and FW was also very high (r = 0.758). There was a negative correlation between the width and height of the foramen magnum and certain dimensions of the skull. The highest negative value was seen between FMW and OA (r = -0.567). The correlation value between FMH and SH was -0.488. These two correlations were statistically significant.
The width and length of the cornual processes in male animals were 35.9 ± 12 mm and 151 ± 78.98 mm, respectively. The correlation between those parameters was very strong (r = 0.997). The correlation coefficient between SH and GLNB was also very high. The correlation value between SH and length of cornual processes was 0.961, the correlation value between the SH and width of cornual processes was 0.945. The correlation coefficient between the greatest length of the nasal bone and the length of cornual processes was 0.956, and correlation between GLNB and width of cornual processes was 0.973.
The values for orbital measurements and the statistical differences between females and males are shown in Table 3. These differences in OD and the percentages of the frontal bone in the orbit perimeter were found to be statistically significant. There was no statistically significant difference in the other measurements of the orbit.
Dimensions of the mandible and the statistical difference levels between females and males are given in Table 4. The mental foramen was situated almost in the middle of the diastema (Fig. 5). LARMF in females was 25.00 mm ± 3.22 and 22.18 mm ± 2.37 in males. This measurement is very helpful to determinate the correct position of the needle during the mental nerve anesthesia.
The distance of mandibular foramen from mandible angle were respectively 35.37 mm ± 9.36 and 31.87 mm ± 3,27 for females and males. Mandibular foramen is easy to access with the help of these two landmarks which are so practical and during the block of mandibular nerve (Fig. 6).The most important difference was seen in RBMFRMRM, ASL and LARMF. It was observed that the values of females were higher than males in mandible length (ML) as well as in skull length (SL), and these differences were statistically significant. It was observed that the diastema (D) was longer in females; however, the difference between sexes was not significant.
The results of indices are given in Table 5. FMI and OI were bigger in males, while other indices were higher in females. There was no statistical difference between male and female in all index values.
The widest parameter of the skull was the facial width (FW), respectively, 117.42 mm ± 7.45 in males and 120.32 mm ± 4.86 in females, with statistically significant difference between the sexes.

Morphology
In the skull of Sharri sheep as in all ruminants we can distinguish five surfaces: roof of the skull, nuchal plane, base of the skull and two lateral walls. The roof of the skull is formed by incisive, nasal and frontal bones (Fig. 1). The frontal bones comprise most of the roof with double supraorbital foramina in 14 samples (41%) (in only one sample this foramen was very large). In 10 female skulls (29% of the total samples) we observed a concave surface like fossa in the midline between two frontal bones rostrally to supraorbital foramina. All female skulls were without cornual processes and the small elliptic, smooth area-fossa postorbitalis, described by Gündemir et al. (2020) in Bardhoka sheep, was absent in all samples. In either site of frontal bones just behind the caudal wall of the orbits and on opposite sides of the supraorbital foramen, a large fossa was present in eight female skulls (23%). The nuchal plane was composed by squama and lateral parts of the occipital bone and the parietal plane of the parietal bone (Fig. 3). The foramen magnum almost round, was situated between two ellipsoid condyles. Inter base precondylar width (IBPCW) was significantly different between sexes ( Table 2). The coronary suture was "V" shaped in all but eight females and two males (about 30%), where it was instead straight (Fig. 7) similar to a goat´s skull.
The base of the skull is formed by incisive, maxilla, palatine, pterygoid, sphenoid and occipital bones (Fig. 4). The muscular tubercles of occipital bone were very large and elongated in 15 cases (44%). Rostrally and between two palatine processes of the maxilla in 9 samples (26%) one elongated fossa was visible. In 10 skulls (30%), the two vertical plates of the palatine bones joined in the mid line with its horizontal plate in a "V" shape, while the rest of the skulls joined in the shape between "V" and "U.
Ventrally, two condyles were joined with a notch between them. A narrow intercondylar notch has been distinguished in eight skulls (about 24%), and a large notch has been seen in eight samples. The rest (almost 50%) of the samples were average.
In seven skulls (20%), the oval foramen was very large and the sphenopalatine foramen was smaller. Other individuals had smaller oval foramen and very large sphenopalatine foramen. The muscular processes of the temporal bone were double in eight cases (24%).
Lateral walls of the skull are formed by incisive, maxilla, zygomatic, lacrimal, parietal and temporal bones (Fig. 2). Only eight female skulls (23%) had prominent male profile, while none of the male skulls had a male profile. In the union of lacrimal bone, the maxilla and nasal bone on either side are elongated, and there is a narrow nasomaxillary fissure and nasolacrimal fissure (Constantinescu 2018). In 15 samples (44%) these two fissures were fused and only in two cases small intra sutural bones between these two fissures were observed. On the lateral surface of the maxilla, multiple very large (11-17 mm) infraorbital foramina were located. In eight samples (23%), they were smaller (6-8 mm) and round. In all skulls, a very prominent external lacrimal fossa was found between the lacrimal and zygomatic bones. The orbits were well developed with almost equal vertical and horizontal diameters. The orbital ring was formed by: zygomatic bone ventrally (37.41%), lacrimal bone rostrally (17.81%) and frontal bone dorso-caudally-the biggest part (48.43% of the total perimeter length) ( Table 3). The frontal part of the orbits showed differences between the sexes.
Just laterally at the base of the zygomatic process of the temporal bone the osseous part of the external acoustic meatus was located (Constantinescu 2018;König and Liebich 2020).

Discussion
With the studies on the skeletal system, knowledge on taxonomy was obtained, and with the help of these measurements, the differences regarding gender analysis were revealed. In this study, 51 parameters were measured on the skull and mandible of the Sharri sheep. It was observed that 13 of these parameters made a statistical difference in sex determination. In addition, five different indices were evaluated and none of them were statistically different between females and males. The skull was also examined morphologically in the study. Sections that make a difference between male and female were specified.
The nasal bones were convex and the nasofrontal suture was between a "V" and "U" shape, compare to the nasofrontal suture in Mehraban sheep which is "U" shaped (Karimi et al. 2011) or in Bardhoka sheep which is "V" shaped ). The palatomaxillary suture was "V" shaped like in the Bardhoka .
Skull length (SL) is an important parameter and has therefore been evaluated in many studies. It is thought that this parameter may help taxonomic classification between species. In one study of Onuk et al. (2013) craniometric data of three species of ruminants were obtained, and the difference between these species was statistically evidenced. Similar observations were made in relation to European bison (Krasińska et al. 2008;Kobryńczuk et al. 2008a). It is stated in the literature that the parameter of skull length was 241.30 ± 14.01 mm in Turkish-origin İvesi sheep (Yılmaz and Demircioglu 2020), 241.20 ± 25.17 mm in Hemşin sheep (Dalga et al. 2018), 204.49 ± 9.71 mm in Morkaraman sheep and 198.09 ± 7.69 mm in Tuj sheep (Özcan et al. 2010). In the study conducted in Trinidad, the skull length of Barbados Black Belly Sheep was 24.65 ± 2.16 cm (Mohamed et al. 2016). In case of Iranian Mehraban sheep, the skull length was reported to be 20.06 cm (Karimi et al. 2011). It was said that this length was 325 ± 9.9 mm in Yankasa rams of Nigerian origin (Shehu et al. 2019) and 265.51 ± 22.24 mm in Xisqueta sheep of Spain (Parés Casanova et al. 2010). In the Bardhoka sheep breed of Kosovo origin , this value is said to be 245.25 ± 10.24 mm for females and 257.98 ± 15.81 mm for males.