THE THORAX — THE OCCIPITAL BONE 



47 



THE THORAX 

 The bony thorax of the horse is remarkably compressed laterally in its anterior 

 part, but widens greatly behind. The anterior aperture is oval and very narrow 

 below; in a horse of medium size its greatest width is about 4 inches (10 cm.), and 

 its height 7 to 8 inches (ca. 18 to 20 cm.). The ventral wall or floor is about 16 

 inches (40 cm.) long, and the dorsal wall or roof about 38 to 40 inches (95 to 100 

 cm.) long. The height from the last segment of the sternum to the seventh or 

 eighth thoracic vertebra is about twice that of the anterior aperture ; this is due to 

 the obliquity and divergence of the roof and floor. The greatest width of the pos- 

 terior aperture is about 20 to 24 inches (50 to 60 cm.). The intercostal spaces 

 increase in width from the first to the seventh or eighth, and then diminish. Their 

 average width is about 13^ to 13^ inches (3 to 3.5 cm.). 



The Bones of the Skull 

 (a) bones of the cranium 



The bones of the cranium (Ossa cranii) are the Occipital, Sphenoid, Ethmoid, 

 Interparietal, Parietal, Frontal, and Temporal. The first four are single, the others 

 paired. 



Occipital 



poral 



Mental forame 



.Incisor 



teeth 



Fig. 26. — Skull, Atlas, and Axis of Horse, Lateral View. 

 8, Body of mandible; 28', horizontal (molar) part of ramus; ,30, vertical part of ramus; 9, zygomatic 

 process of squamous temporal; 11, coronoid process of mandible; 12, supraorbital process; 13", paramastoid 

 (styloid) process of occipital; 19, orbit; 20, malar bone; 21, lacrimal bone; 22, nasal bone; 23, premaxilla; 

 23', nasal process of premaxilla; 2.5, 29, canine teeth; 26, maxilla; 27, facial crest; 31, condyle of mandible; 

 32, atlas; 33, axis; x, wing of atlas; e, naso-maxillary notch. (After Ellenberger-Baum, Anat. fiir Kiinstler.) 



The Occipital Bone 

 The occipital bone (Os occipitale) is situated at the posterior part of the cra- 

 nium, of which it forms the posterior wall and part of the ventral wall or base/ 

 'The long axis of the skull is considered to be horizontal in these descriptions. 



