THE HEAD. 



Fig. 20. 



lamina of the ethmoid bone. The very thin lateral portions form part of the 

 circumference of the wings ; they are notched near their union with the 

 middle piece to assist in the formation 

 of the orbital foramen. The two lateral 

 borders are thin and convex in their an- 

 terior half, as is also the contour of the 

 wings, which are mortised in the frontal 

 bone. For the remainder of their extent 

 they are thick, denticulated, and bevelled 

 at the expense of the external plate, to 

 articulate with the squamous portion of 

 the temporal bone. 



Structure. This bone is compact on 

 its sides, and spongy in its middle part ; 

 inferiorly, it is excavated by the sphe- 

 noidal sinuses. 



Development. It is developed from 

 two principal nuclei of ossification ; a 

 superior forms the subsphenoidal pro- 

 cess and the canal of the same name, 

 the vidian fissure, pituitary fossa, fissures 

 of the internal face, and the most pos- 

 terior of the great supersphenoidal 

 canals ; the other, the inferior, forms that 

 portion of the body hollowed by the 

 sinuses, the lateral alas, 1 and the optic 

 fossa and canals. In meeting each 

 other, these centres form the vidian canal 

 and the two anterior supersphenoidal 

 canals. They are not consolidated with 

 each other until a very late period ; for 

 which reason they are sometimes de- 

 scribed as two distinct bones. M. POSTERIOR BONES OF THE HEAD OF A 

 Tabourm has even proposed to attach FCETUS (HORSE) AT BIRTH; DISARTICU- 

 the description of the inferior sphenoid LATED AND VIEWED IN FRONT. 

 to that of the ethmoid, because it is A, Sphenoid bone, 1, Maxillary notch ; 2, 



united with this bone a long time before 

 it is joined to the superior portion. 



Carotid notch ; 3, Groove for the passage 

 of the maxillary nerve; 4, Cavernous 

 sinus; 5, Optic fossa; 6, Great wing; 

 6', Unossified portion of the great wing ; 

 7, Notch for the formation of the orbital 

 foramen. B, Vomer. C, Palate bone. 

 D, Zygoma. E, Superior maxilla. 8, In- 

 ferior orifice of the maxillo-dental canal. 

 F, Premaxillary bone. 



6. Temporal Bone. 



The temporal bones inclose the 

 cranial cavity laterally, and articulate 

 with the occipital, parietal, frontal, 

 sphenoidal, and the zygomatic bones; 

 also with the inferior maxilla and the hyoid bone. Each is divided into 

 two pieces, which are never consolidated in the horse ; one forms the 

 squamous portion of the temporal bone ; the other, the tuberous portion. They 

 will be described separately. 



Squamous Portion. This is flattened on both sides, oval, and slightly 

 incurvated like a shell, a shape to which it owes its name. It offers for 

 study an external and an internal face., and a circumference. 



1 These wings are not analogous to those portions of the sphenoid bone in Man bear- 

 ing the same name. They are the processes of Ingrassias enormously developed. 



