THE SKULL AS A WHOLE 75 
extreme anterior part is the fossa for the lacrimal sac. Behind this there is a small 
depression in which the inferior oblique muscle of the eye arises; here the plate 
which separates the orbit from the maxillary sinus is very thin. The dorsal wall 
(Paries dorsalis) is formed by the frontal and to a small extent by the lacrimal bone. 
It presents the supraorbital foramen, which perforates the root of the supraorbital 
process. The ventral wall (Paries ventralis) is very incomplete, and is formed by 
the malar, the zygomatic process of the temporal, and to a small extent by the max- 
illa. The lateral wall (Paries lateralis) is the supraorbital process. At the extreme 
posterior part is the orbital group of foramina. Four are situated in front of the 
pterygoid crest. Of these, the uppermost is the ethmoidal foramen, which trans- 
Fic. 48.—CRanNIAL AND OnbiTAL Recions oF SkuLL oF Horse; Larerat View. Tue Zyrcomatic ARCH AND SuPRA- 
ORBITAL Process Have BEEN Sawn OFF. 
S.o., Squamous part of occipital; P, parietal; S, squamous temporal; B.o., basilar part of occipital; B.s., body of 
sphenoid; A.t., temporal wing of sphenoid; A.o., orbital wing of sphenoid; Pt.p., pterygoid process of sphenoid; P-.p., 
perpendicular part of palate bone; F, F’, facial and orbital parts of frontal bone; L, L’, orbital and facial parts of lacri- 
mal bone; M, facial part of malar bone; M.z., maxilla; a, parieto-occipital suture; b, squamous suture; c, d, spheno- 
Squamous suture; e, fronto-palatine suture; /, fronto-lacrimal suture. 1, Occipital condyle; 2, condyloid fossa; 3, 
paramastoid process; 4, nuchal crest; 5, external occipital protuberance; 6, external acoustic meatus; 7, mastoid 
proc 8, hyoid process; 9, stylomastoid foramen; 10, muscular process; 11, foramen lacerum; 12, postglenoid 
process; 13, glenoid cavity; 14, temporal condyle; 15, pterygoid groove; 16, alar canal of pterygoid process indicated 
by arrow; 17, alar foramen; 18, ethmoidal foramen; 19, optic foramen; 20, foramen,erbitale; 21, maxillary fora- 
men; 22, sphenopalatine foramen; 23, posterior palatine foramen; 24, supraorbital foramen (opened); 25, fossa for 
lacrimal sac; 26, depression for origin of obliquus oculi inferior; 27, facial crest; 28, maxillary tuberosity; 29, alveolar 
tuberosity; 30, hamulus of pterygoid bone. 
mits the ethmoidal vessels and nerve. The optic foramen is situated a little lower 
and further back; it transmits the optic nerve. Immediately below the optic is 
the foramen orbitale, which transmits the ophthalmic, third, sixth, and sometimes 
the fourth nerve; commonly there is a very small trochlear foramen in the crest 
for the last-named nerve. The foramen rotundum is below the foramen orbitale, 
from which it is separated by a thin plate; it transmits the maxillary nerve. The 
alar canal opens in common with the foramen rotundum, and the anterior opening 
of the pterygoid canal is also found here. The foramen alare parvum is just be- 
hind the pterygoid crest and on a level with the foramen orbitale. It is the upper 
opening of a canal which leads from the alar canal, and through it the anterior deep 
