70 



THE SKELETON OF THE HORSE 



The superior wall or roof (Calvaria) is formed })y the supraoccipital, inter- 

 parietal, parietal, and frontal bones. In the middle line is the internal sagittal 

 crest, which joins the crista galli in front, and furnishes attachment to the falx 

 cere])ri. Posteriorly the crest is continued by the sharp anterior margin of the 

 tentorium osseum, which projects downward and forward into the cavity, and gives 

 attachment to the tentorium cerebelli by its sharp lateral edges. Behind this the 

 roof is grooved centrally for the middle lobe or vermis of the cerebellum. Trans- 

 verse grooves pass from the base 

 of the tentorium osseum to the 

 parieto-temjjoral canals. The 

 anterior part of the roof is hol- 

 lowed by the frontal sinus. The 

 occipital part is very thick and 

 strong. 



The lateral walls are formed 

 by the occipital, parietal, tem- 

 poral, and frontal bones, and in 

 part by the orbital wings of the 

 sphenoid. Each is crossed oli- 

 liquely by the petrosal crest, 

 which concurs with the project- 

 ing margin of the ]3arietal bone 

 and the tentorium osseum in 

 dividing the cavity into cerebral 

 and cerebellar compartments. 

 Behind the crest is a depression 

 for the lateral lobe (hemisphere) 

 of the cerebellum. Below this 

 are the internal auditory meatus 

 and the openings of the aquse- 

 ductus vesti])uli and aquaeductus 

 cochleiB. 



The roof and lateral walls 

 are marked by digital impres- 

 sions and vascular grooves. 



The inferior wall or floor 

 (Basis cranii interna) may be 

 regarded as forming three fossae. 

 The anterior fossa (Fossa cranii 

 anterior) supports the frontal and 

 olfactory parts of the cereljrum. 

 It is formed chiefly by the pre- 

 sphenoid, and lies at a higher 

 level than the middle fossa. In 

 front the fossa is divided medi- 

 ally by the crista galli, lateral to 

 which are the deep ethmoidal or 

 olfactory fossae for the olfactory 

 lobes. The ethmoidal or internal orbital foramen perforates the cranial wall 

 at the outer side of these fossse. Further back the central part of the surface 

 is slightly elevated, and is flanked by shallow depressions which support the ol- 

 factory peduncles. Posteriorly is a bony shelf which covers the entrance to the 

 optic foramina ; the edge of this shelf and the posterior borders of the orbital wings 

 of tlui sphenoid may be taken as the line of demarcation between the anterior and 



Fig. 35. — Floor of Cranial Cavity of Horse. 



The roots of the cranial nerves are shown on the left side 

 and are designated by number. /, Anterior cranial fossa; //, 

 middle cranial fossa; ///, posterior cranial fossa; a, ethmoidal 

 fossa; 6, ethmoidal foramen; c, foramen for nasal branch of 

 ophthalmic artery; d, orbital wing of sphenoid bone; c, optic 

 fossa; /, sella turcica; g, spheno-occipital crest; h, h', clotted line 

 indicating contour of pituitary body; h", slight elevation repre- 

 senting dorsum sells; i, k, grooves for nerves and cavernous 

 sinus; I, depression for pyriform lobe of cerebrum; m, groove 

 for middle meningeal artery; n, depression for pons; o, foramen 

 lacerum anterius; p, foramen lacerum posterius; q, incisura 

 carotica; </, incisura ovalis; (f, incisura spinosa; )•, depression 

 for medulla oblongata; s, hypoglossal foramen; t, internal audi- 

 tory meatiis; u, foramen magnum; r, frontal sinus; w, zygomatic 

 process of temporal bone; x, section of petrous temporal; y, 

 section of occipital bone; z, crista galli; 1, 1', 1", dotted lines 

 indicating position of olfactory tracts and peduncle. (After 

 EUenberger-Baum, Top. Anat. d. Pferdes.) 



