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 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 Paulli) the sphenoidal and palatine parts are separated by a transverse 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 ethmoturbinal. It communicates with the maxillary sinus. [Illustration: FIG. 40.—SKULL OF HORSE, DORSAL VIEW, WITH SINUSES EXPOSED BY REMOVAL OF THE OUTER PLATE OF BONE. _1_, Frontal bone; _2_, 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_, fronto-maxillary opening; _f_, naso-maxillary opening below plate which forms the anterior margin of _e_; _g_, _h_, posterior and anterior compartments of maxillary sinus—often called the superior and inferior maxillary sinuses; _i_, septum between _g_ and _h_; _k_, orbit; _l_, 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.