142 



THE BONES. 



LEG-BONES OF THE MULE, WITH THE 

 FIBULA COMPLETELY DETACHED. 



I, Nutrient foramen ; 2, insertion sur- 

 face for the perforans ; 3, insertion 

 surface for the popliteus ; 4, tibial 

 ridge ; 5, fossa for the insertion of 

 the anterior crucial ligament; 6, in- 

 ternal articular surface; 7, external 

 articular surface ; 8, tubercle for the 

 insertion of the posterior crucial liga- 

 ment ; 9, fossa for the insertion of 

 the internal meniscus ; 10, tibial 

 crest ; 11, internal and inferior tu- 

 berosity; 12, external and inferior 

 fissure of the tuberosity; 13, pos- 

 terior prominence formed behind by 

 the median spur of the inferior articu- 

 lar surface ;' 14, superior extremity 

 of the fibula articulating with the 

 tibia; 15, the body ofthe fibula — com- 

 pletely developed in this specimen. 



middle by a vertical fissure. The infernal 

 tubcrosif//,^ better defined, is margined pos- 

 teriorly by an oblique channel. 



Structure and development. — The tibia is 

 very compact in its inferior portion, and is 

 developed from five chief centres of ossifica- 

 tion. The body is formed by one and the 

 superior extremity by two, the anterior tuber- 

 osity having one of these ; the last develops 

 the whole of the inferior extremity of the bone, 

 except the external tuberosity, which is de- 

 veloped from a separate nucleus, that at an 

 early period becomes fused with the principal 

 one of the epiphysis. 



The tibia of the Ass is remarkable for 

 the more or less perfect equality of the promin- 

 ences around the inferior articular surface, so 

 that this bone can sometimes lie in stable 

 equilibrium on its inferior extremity. It is 

 also distinguished from that of the Horse by : 



1. The more or less marked obliquity of the 

 grooves which articulate with the astragalus. 



2. The disposition of the oblique prominence 

 coursing the surface, for the insertion of the 

 popliteus muscle. 3. The great development 

 of the imprint for the semitendinosus muscle, 

 and the crest above the groove for the oblique 

 flexor tendon of the phalanges. 



The tibia of the Mule and Hinny more 

 particularly resembles that of the Horse. 



2. Fibula, ok Peroneus (Fig. 94). 



A small, undeveloped bone, elongated and 

 styloid in shape, situated outside the tibia, 

 and extending from the superior extremity of 

 that bone to the middle or lower third of its 

 body. 



The middle portion of the fibula is thin 

 and cylindrical, and forms above, in common 

 with the external border of the larger bone, 

 the tibial arch. Its superior extremity, wide 

 and flattened on both sides, has received the 

 name of head. It offers, on its internal face, 

 a diarthrodial facet to articulate with the 

 external and superior tuberosity of the tibia ; 

 on its external face it shows ligamentous im- 

 prints. The infei'ior extremity of the fibula 



* The internal malleolus. 



