86 THE BONES. 



THE SMALL SESAMOID (OB NAVICULAR) BONE. This short bone is annexed 

 to the third phalanx, behind which it is situated ; it is elongated transversely, 

 flattened above and below, and narrowed at its extremities. It offers : 1, A 

 superior face, on which are prolonged the glenoid cavities and the median ridge 

 of the articular surface of the os pedis ; it responds to the second phalanx ; 

 jr,g 51 2, An inferior face, divided by a 



slight relief into two undulated 

 facets, and covered with cartilage 

 ~ii to form a gliding surface ; 3, An 

 anterior border* channeled length- 

 ways by a groove of insertion, above 



NAVICULAR BONE. which is remarked a diarthrodial 



a, Upper, or articular surface /6, inferior border; &cet t^t brings the small sesa- 

 c, Superior border; d, Inferior, or posterior moid into contact with the pos- | 

 surface ; e, The median transverse ridge ; /, terior border of the third phalanx ; 

 Inferior margin; 0, Superior margin. ^ A poster i or border and two ex- 



tremities, for ligamentous insertion. This bone, as well as the sesamoids, 

 originates from a single centre of ossification. It is formed of a layer of 

 compact tissue enveloping a nucleus of very condensed spongy substance. 



DIFFERENTIAL CHARACTERS OF THE ANTERIOR LIMB IN OTHER THAN SOLIPED 



ANIMALS. 



A. SHOULDER. In Carnivora the shoulder is composed of two bones, these creatures 

 being furnished with a clavicle. This bone in the Dog is a little osseous shell imbedded 

 among the muscles situated in front of the Bcapulo-humeral angle. That of the Cat 

 constitutes a small sstyloid bone, which is joined to the acromion and sternum by two 

 ligamentous cords. 



In all the domesticated animals except Solipeds, the coracoid process is immediately 

 applied against the glenoid cavity. In all, al*o, with the exception of the Pig, the 

 scapular spine gradually rises from above to below, and terminates in a sharp salient 

 point, the acromion. 



The sp;ne partitions the external face of the bone into two equal fossae in the Dog, 

 and in Ruminants into two fossae, which, for extent, are as one to three to each other. 

 The scapular spine of the Pig is much elevated towards the middle part, and bends more 

 or less backwards, 



In the Carnivora the prolonging cartilage is entirely absent; the anterior border of 

 the scapula is very convex, as if the bone had been curved downwards. In the other 

 domesticated mammals the scapula is somewhat regularly triangular. 



B. ARM. Proportionately, the humerus is longer, and move inflected like an S, as 

 the number of apparent digits is increased. Therefore it is that in the Carnivora the 

 characters of length and inflexion are most marked. 



In the Ox, Sheep, Pig, and Dog, the furrow of torsion is not so deep as in the Horse, 

 and the deltoid imprint is less salient. In the Dog this imprint is represented by a large 

 roughened surface; in the Pig by some asperities only. The nutrient foramen is on 

 the posterior face. It has been stated that the medullary canal in the Ox is traversed by 

 an osseous band; but the presence of this is not constant. 



The summit of the trochiter is very elevated, particularly in Ruminants, and is thrown 

 back OH the bicipiial groove, which is single; in the Dog and Pig, this groove is carried 

 inwards iibove the internal face of the humerus. 



The external trochlea in the Ox and Pig is well marked. In Carnivora, the inner lip 

 of this trochlea is very high, and the external lip incomplete; a foramen establishes 

 communication between the olecranian and coronoid fossa3. in the Cat there is found, on 

 the inner side of the lower extremity, a particular foramen that forms a vascular arch. 



C. FORE-ARM. The fore-arm is short in the Ox, Sheep, and Pig , very long in the 

 Carnivora. The principal differential characters that it presents are connected with the 

 relative dimensions of the two bones and their nvde of union. Regarding these, and as 

 generally applicable, the following principles may be laid down : 



1. Tiie development of the ulna is in direct relation to the division of the foot. Mono- 

 dactyloua animal, such as the Horse, Ass, and Mule, have in fact only a rudimentary 



