146 SKELETON OF THE PIG 



the roof and almost all of the sides of the cranium, and extends forward into the 

 roof of the nasal cavity a variable distance — sometimes as far as a transverse plane 

 through the infraorbital foramina. The septum between the right and left sinuses 

 is usually deflected in an irregular manner in its middle part, but is practically 

 median at either end. Each sinus is subdivided by numerous septa, some of which 

 are complete. Thus the sinus is divided into compartments, each of which com- 

 municates with an ethmoidal meatus. 



In the young pig the sinus is small and is confined to the anterior part of the frontal Ijone. 

 Later it extends backward, outward, and to a less extent forward. In the old subject it penetrates 

 laterally into the supraorbital process and the root of the zygomatic process of the temporal bone, 

 and behind almost down to the foramen magnum and the occipital condyles. It then consists 

 of six to eight compartments usually. 



The maxillary sinus is relatively small. Its anterior end is a little less than 

 an inch (ca. 2 cm.) behind the infraorbital foramen, and it extends upward into 

 the lacrimal and backward into the malar bone. The infraorbital canal passes 

 along its floor, and the roots of the molar teeth do not project up into it. It does 

 not communicate with the frontal and sphenoidal sinuses, but with the posterior 

 part of the middle meatus by means of a consideral)le orifice. 



The sphenoidal sinus is very large. It involves the body, pterygoid processes, 

 and temporal wings of the sphenoid bone, and extends into the squamous temporal. 

 It communicates with the ventral ethmoidal meatus. 



There is a small sinus in the perpendicular part of the palate bone which com- 

 municates with an ethmoidal meatus. 



BONES OF THE THORACIC LIMB 



The scapula is very wide, the index being about 1 :0.7. The spine is tri- 

 angular and is very wide in its middle, wdiich curves backward over the infra- 

 spinous fossa and bears a large tuberosity. Its lower part bears a small projection 

 (rudimentary acromion). The anterior border is strongly convex in profile, sinuous 

 when viewed from the front, and thick and rough in its middle. The posterior 

 border is wide, slightly concave, and bears an outer rough lip. The vertebral 

 border is convex, and the cartilage is not so extensive as in the horse and ox. The 

 cervical angle is thin and bent inward a little. The dorsal angle is thick and is 

 about a right angle. The neck is wefl defined. The rim of the glenoid cavity is 

 rounded and not notched. The tuberosity is just above the antero-internal part 

 of the glenoid cavity and bears no distinct coracoid process. 



The humerus has an appearance in profile somewhat like an italic / minus the 

 cross-bar; this is due to the marked backward and forward inclination of the prox- 

 imal and distal ends respectively. The shaft is decidedly compressed from side to 

 side. The internal surface is extensive and flattened; it is separated from the 

 anterior surface by a distinct l^order, and bears no teres tubercle. The musculo- 

 spiral groove is shallow. The deltoid tuberosity is small, and there is a larger 

 rounded eminence midway lietween it and the external tuberosity. The nutrient 

 foramen is on the posterior surface below its middle. The head is more strongly 

 curved and the neck better marked than in the horse or ox. The external tuber- 

 osity is very large and extends upon the front of the extremity. It is divided into 

 two high prominences by a wide deep groove. There is a third eminence below 

 and externally for the attachment of the supras]iinatus muscle. The bicipital 

 groove is at the front of the inner side ; it is undivided and is almost converted into 

 a canal. The outer groove on the distal articular surface is so shallow as to give 

 the appearance of two condyles of similar size. The olecranon fossa is very deep, 

 and the plate of bone which separates it from the coronoid fossa is thin and some- 



