358 ANATOMY OF VERTEBRATES. 



and gives passage to the vessels of the Harderian gland lodged in 

 the wide and deep acetabular fossa. 



The femur is a straight, or nearly straight, long, cylindrical 

 bone, having a hemispherical head supported on a very short 

 neck, especially in the Petaurists, and situated here almost in the 

 axis of the shaft, above and between the two trochanters, which 

 are nearly of equal size. In the Kangaroos and Potoroos the 

 head of the thigh-bone is turned more inward, and the outer or 

 greater trochanter rises above it. In other Marsupials the great 

 trochanter is less developed. In most of the species a strong 

 rid2:e is continued downward to within a short distance from the 

 trochanter, and this ridge is so produced at the lower part in the 

 Wombat as almost to merit the name of a third trochanter. In the 

 Wombat and Koala there is no depression for a ligamentum teres. 

 The shaft of the bone presents no linea aspera. 



The canal for the nutrient artery commences at the upper third 

 and posterior part of the bone in the Koala, and extends down- 

 ward, contrarimse to that in most other marsupial and placental 

 Mammalia. 



At the distal extremity of the femur the external condyle is 

 the largest, the internal rather the longest. The intermediate 

 anterior groove for the patella is well marked in the Perameles, 

 where the patella is fully developed, but is broad and very shallow 

 in the Phalangers and Dasyures, where the tendon of the rectus 

 muscle is merely thickened or offers only a few irregular specks 

 of ossification ; and the corresponding surface in the Petaurists, 

 Wombat, and Koala is almost plane from side to side ; in these 

 Marsupials and in the Myrmecobius the patella is wanting. I 

 find a distinct but small bony patella in the Macropus Bennettii. 

 There is a sesamoid bone above and behind the external condyle 

 of the femur in the Myrmecobius and some other Marsupials. 



In the knee-joint, besides the two crucial ligaments continued 

 from the posterior angles or cresses of the semilunar cartilages — 

 one to the outer side of the inner condyle, the other to the inter- 

 space of the condyles — there is a strong ligament which passes 

 from the anterior part of the tibial protuberance backward to 

 the inner side of the fibular condyle, and a second continued from 

 the same point along the outer margin of the outer semilunar 

 cartilage to the head of the tibia. 



The tihia, fig. 228, 66, presents the usual disposition of the arti- 

 cular surface for the condyles of the femur, but in some genera, 

 as the Wombat and Koala, the outer articular surface is con- 

 tinuous with that of the head of the fibula. In the Kangaroos 



