ANATOMY OF THE HORSE. 19 



raences the cavity of the pelvis, which again is bounded poste- 

 riorly by the outlet. The lateral walls of the cavity are formed 

 principally by the ilea; the ischia and pubes, united at their 

 symphyses, including the obturator foramina, are mostly con- 

 sumed in completing the cavity below ; while the sacrum alone 

 constitutes the superior boundary. The supero-inferior diameter 

 of the brim in the young subject exceeds the lateral ; in the 

 adult mare these two diameters, and also the antero-posterior 

 length of the cavity, measuring from the brim to the extreme 

 points of the ischiatic tuberosities, are about equal — about ten 

 inches. 



The Inlet displays — laterally, the ilea, with their thin project- 

 ing anterior spinous processes; superiorly, the promontory of the 

 sacrum and the sacro-iliac articulations ; inferiorly, the grooves 

 for the psoas and iliacus, and the symphysis pubis. 



The Outlet presents three notches : two lateral, very exten- 

 sive ; one middle, considerably smaller. The two former, named 

 the great sciatic notches, constituted by the posterior borders 

 of the ileum and ischium and the sides of the sacrum, are prin- 

 cipally occupied by the sciatic ligaments, although they give 

 transit to the pyramidal muscles, the gluteal and obturator ves- 

 sels, and the sciatic nerves. The middle notch is the pubic 

 arch, formed by the divergence of the ischiatic tuberosities : it 

 is occupied in either sex by the urinary canal. 



OF THE HEAD. 



The head is an oblong quadrangular form, broad and flatten- 

 ed on its sides, narrow and contracted anteriorly and superiorly, 

 bulky at the opposite points, hollow interiorly. It is remarkable 

 for the prolongation and capaciousness of the parts devoted to 

 the formation of the nose and mouth, and for the diminished 

 sphere of the cranium. It constitutes the anteriormost part of 

 the skeleton, is articulated with the spine by which it is sus- 

 pended, and is divided into cranium and face. 



I.— THE CRANIUM. 



The cranium or brain-case is but small when compared with 

 the bulk of the body in general : it forms the supero-posterior 

 part of the head ; is prominent and convex, superiorly and late- 

 rally ; irregular and in places open, inferiorly ; hollow and vault- 

 ed, within. It is composed of ten pieces — three pairs and four 

 single bones; viz. superiorly and anteriorly, of the two frontals ; 

 superiorly and in the middle, of the parietal ; superiorly and 



