48 THE BONES. 



the anterior lateral from the corresponding posterior lateral border, and are occupied 

 by the petrous portion of the temporal bone. 



Structure. — The occipital bone contains much spongy substance. 



Development. — It is developed from four centres of ossification ; one, the 

 anterior, is single, and forms the occipital tuberosity ; another, the posterior, 

 also single, forms the basilar process ; the other two are pairs, and comprise each 

 a condyle, with a styloid process and the corresponding condyloid foramen. 



The occipital bone in the Ass is distinguished by the prominence of the 

 external occipital tuberosity (see the Head in CTeneral), by the depth of the 

 groove (mastoid) which courses over the outer face of the styloid process, and 

 by the articular surface prolonged to the origin of the basilar process, which 

 constricts it in a circular manner. 



Differential Chaeacters in the Occipital Bone of other Animals. 



A. Ox. — The occipital bone of this animal does not show any anterior elbow, neither does 

 it form a portion of the anterior part of the head. The external occipital tuberosity is obtuse> 

 and gives rise on each side to the superior curved lines. 



The styloid processes are short and much bent inwards. The basilar process, wide, short, 

 and thick, has a groove in the middle of its external face ; this groove is sometimes absent in 

 the Sheep and Goat. 



The condyloid foramina are double, sometimes triple ; the superior foramen does not pass 

 directly into the cranium, but goes to a vast conduit tliat opens behind on the lateral margin 

 of the occipital foramen, and wliich terminates in front by twi) orifices, one entering the parieto- 

 temporal canal, the other opening on the external surfiice of the bone. The foramen lacerum 

 is divided into an anterior and posterior forameu, by the mastoid portion of the temporal 

 bone. 



B. Sheep and Goat. — The inner tuberosity is only marked by a slight prominence of the 

 internal plate of the bone. In the occipital bone of these animals are found the peculiarities 

 noted in that of the Ox ; the groove on the basilar process is sometimes absent, and in the 

 Sheep the superior curved lines are very salient and occupy the summit of the head. Tnis 

 feature is still more marked in the Goat, and also more in the Cervine species, in which this 

 bone Somewhat re.'^embles that of the Horse. 



C. Camel. — The bone shows a double angle as in Solipeds. In its anterior and .-uperior 

 portions it resembles that of the Horse, and in its posterior portion that of the Ox. The crest, 

 which constitutes the origin of the parietal crests, as well as the superior curved lines, are 

 thin, sharp, and very high. The styloid processes are short, wide, thick, and articulated by 

 harmonic suture with the tuberosity of the temporal bone. The superior curved lines are 

 scarcely marked in young animals. 



D. Pig. — The occipitnl bone in this animal is not bent anteriorly; but the transverse 

 protuberance representing the curved lines forms, nevertheless, as in the Horse, the summit of 

 the Head. This eminence, which is excavated on both s-ide-s on the posterior face, unites in 

 front with the parietal bone, which abuts on the occipital at an acute angle. There is no 

 external occipital protuberance, properly speaking, and the styloid processes are very long and 

 directed downwards. 



E. Carnivora. — The external occipitnl tuberosity is very strong and high. The external 

 occipital crest is absent or little marked ; the styloid procc sscs are short. The furamen lacerum 

 is divided into two portions by the mastoid process, and the basilar prociss is wide, long, and 

 thick, and hollowed on the side by a cliannel tliat joins a similar one in the temporal bone to 

 form a large venous canal. This last communicates, behind, with the posterior foramen 

 lacerum, and opens, in front, in the cranium, where it is continuous with the cavernous groove 

 of the sphenoid. The anterior angle forms a very marked prominence, which is deeply fixed 

 into the parietal bone, and partly constitutes the internal occipit .1 process of that bone. The 

 latter does not show the lateral excavations at its base; they are found lower, towards tiie 

 summit of the petrous bone, on the sides of the occipital. The parieto-temporal canals are, 

 nevertheless, continued to the base of the process, which they traverse to open into its interior. 

 In the most intelligent breeds, the occipital foramen is deeply notched above (Faure). 



