74 



THE SKELETON OF THE HORSE 



plane through the anterior margins of the orbits, l^ackward to one through the t 

 poral condyles, and outward into the root of the supraorbital process. It is sej 



ated from the sinus of the opposite side b> 

 complete septum. It is partially subdivided i 

 a number of bony plates. The turbinal part 

 situated in the posterior part of the superior tu^ 

 binal bone, roofed in l)y the nasal and lacrimal 

 bones. It extends forward to a transverse plane 

 about half-way between the anterior margin of 

 the orbit and the end of the facial crest. Be- 

 hind it is in free communication with the 

 frontal part over the lateral mass of the eth- 

 moid. It is separated from the nasal cavity 

 by the thin turbinal plate. The frontal and 

 maxillary sinuses communicate through the 

 large opening described above. 



The spheno-palatine sinus (Sinus spheno- 

 palatinus) consists of two parts which communi- 

 cate under the lateral mass of the ethmoid. 

 The sphenoidal (posterior) part is excavated in 

 the body of the pre-sphenoid. The palatine (an- 

 terior) part is between the two plates of the per- 

 pendicular part of the palate bone, under the 

 lateral mass of the ethmoid; it communicates 

 freely with the maxillary sinus. The septum 

 between the right and left sinuses is not usually 

 median in the sphenoidal part. 



In about one-third of the cases (according to PaulU) 

 the sphenoidal and paUxtine parts are separated by a trans- 

 verse septum, and the sphenoidal part then communicates 

 only with the lower ethmoidal meatuses. 



The term ethmoidal sinus is often applied 

 to the cavity of the largest ethmo-turbinal. It 

 communicates with the maxillary sinus. 



Fig. 40. — Skull of Horse, Dorsal View, 

 WITH Sinuses Exposed by Re- 

 moval OP THE Outer Plate of 

 Bone. 



1, Frontal bone; S, nasal bone; 3, 

 lacrimal bone; 4, maxilla; a, posterior 

 part of frontal sinus; a', middle part of 

 frontal sinus; b, anterior (turbinal) part of 

 frontal sinus; c, lateral mass of ethmoid 

 bone; d, roof of superior meatus; e, fron to- 

 maxillary openinK; /, naso-maxillary oi)pn- 

 ing below plate which forms the anterior 

 margin of e; f/, h, posterior and anterior 

 compartments of maxillary sinus — often 

 called the superior and inferior maxillary 

 sinuses; i, septum between g and h; k, 

 orbit; I, point at which superior turbinal 

 bone may be perforated to obtain drainage 

 into nasal cavity. (After Ellenberger, in 

 Leisering's Atlas.) 



The Bones of the Thoracic Limb 

 the scapula 



The scapula is a flat bone, situated on the 

 anterior part of the lateral wall of the thorax, 

 and extending obliquely from the vertebral end 

 of the seventh or eighth rib to the sternal end of 

 the first rib. It is curved slightly and slopes 

 outward in adaptation to the form of the 

 thoracic wall. It is triangular in outline, and 

 has two surfaces, three borders, and three 

 angles. 



The external surface or dorsum (Facies 



laterahs s. dorsalis) is divided into two fossae 



by the spine (Spina scapulae), which extends 



from the vertebral border to the neck of the 



bone, where it gradually subsides. The free edge of the spine is thick, rough, 



and in great part subcutaneous. A little above its middle is a variable promi- 



