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 obliquely from the fourth thoracie 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 fosse by the spine of 
the seapula (Spina scapula), 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 sping, 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 1s 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 scapule). 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 
