86 THE SKELETON OF THE HORSE 



turbinate plate. The frontal and maxillary sinuses communicate through the 

 large opening described above. 



The sphenopalatine sinus (Sinus sphenopalatinus) consists of two parts which 

 communicate under the lateral mass of the ethmoid. The sphenoidal (posterior) 

 part is excavated in the body of the presphenoid. The palatine (anterior) part is 

 between the two plates of the perpendicular part of the palatine 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 Paulli) the sphenoidal and palatine parts are 

 separated by a transverse septum, and the sphenoidal part then communicates only with the ven- 

 tral ethmoidal meatuses. 



The term ethmoidal sinus is often applied to the cavity of the largest ethmo- 

 turbinate. It communicates with the maxillary sinus through an opening in the 

 lateral lamina. 



The Bones of the Thoracic Limb 

 the scapula 



The scapula is a flat bone which is situated on the anterior part of the lateral- 

 wall of the thorax; its long axis extends obliquelj^ from the fourth thoracic spine 

 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 lateral surface (Facies lateralis) is divided into two fossse by the spine of 

 the scapula (Spina scapulae), which extends from the vertebral border to the neck 

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

 great part subcutaneous. A little above its middle there is a variable prominence, 

 the tuber spinas, to which the trapezius muscle is attached. The supraspinous 

 fossa (Fossa supraspinata) is situated in front of the spine, and the infraspinous 

 fossa (Fossa infraspinata) behind it. The former is much the smaller of the two; 

 it is smooth and is occupied by the supraspinatus muscle. The infraspinous fossa 

 lodges the infraspinatus muscle; it is wide and smooth in its upper part, narrower 

 below, where it is marked by several rough lines for muscular attachment; near 

 the neck is the nutrient foramen, and a little lower is a vascular groove. 



The costal surface (Facies costalis) is hollowed in its length by the subscapular 

 fossa (Fossa subscapularis) ; this occupies nearly the whole of the lower part of the 

 surface, but is pointed above and separates two rough triangular areas (Facies 

 serrata), to which the serratus ventralis is attached. In the lower third there is a 

 vascular groove with several branches. 



The anterior border (Margo cranialis) is convex and rough above, concave and 

 smooth below. 



The posterior border (Margo caudalis) is slightly concave. It is thick and 

 rough in its upper third, thin in its middle, and thickens again below. 



The vertebral border (Margo vertebralis) carries the scapular cartilage (Car- 

 tilago scapulae). In the young subject this edge of the bone is thick, and is pitted 

 by impressions into which the cartilage fits. The cartilage is the unossified part 

 of the foetal scapula. Its lower edge fits the depressions and elevations of the bone. 

 It thins out toward the free edge, which is convex and lies alongside of the vertebral 

 spines. In front it continues the line of the bone, but behind it forms a rounded 

 projection. The lower part of the cartilage undergoes more or less ossification, so 

 that the vertebral border of the bone in old subjects is thin, irregular, and porous. 



The anterior or cervical angle (Angulus cranialis) is at the junction of the 



