282 mb. p. g. parsons on the [Mar. 20, 



ilium just external to the synchondrosis. Its arrangement is very 

 constant. 



Muscles of Posterior Extremity. 



Gluteus Maximus, Tensor Fascice Femoris, and Sartorius. — These 

 three muscles in Eodents are so closely united that they form 

 practically one sheet, which rises from the anterior extremity or 

 crest of the ilium, and from the fascia over the gluteus medius by 

 which they are connected to the spinous processes of the posterior 

 lumbar, sacral, and anterior caudal vertebrae. Occasionally it also 

 rises from the outer part of Poupart's ligament and the inferior 

 border of the ilium. The fibres which rise most anteriorly cross 

 the front of the thigh obliquely, and are inserted into the fascia 

 above and to the inner side of the patella ; these fibres correspond 

 to the sartorius. The fibres rising behind these run down the outer 

 side of the thigh and are inserted into the fascia, there forming the 

 tensor fasciae femoris. The rest of the muscle, or the gluteus 

 maximus proper, is inserted partly into the fascia of the outer side 

 of the thigh, and partly into the femur, sometimes quite high 

 up, at others near its lower end. The nerve supply of these three 

 muscles is the superior gluteal. 



In the Dipodida? few, if any, fibres were noticed going to the 

 femur (Dijrus cegyptius). 



In the Octodontidae the sartorius is well developed, reaching to 

 the patella, while the bony insertion of the gluteus maximus is 

 into the posterior surface of the femur at the junction of the middle 

 and lower thirds (Myopotamus, Capromys, Pilorides, Aulacodus). 



In the Hystricidae the arrangement is the same, except in 

 Sphingurus, in which the insertion of the gluteus maximus is into 

 the middle of the femur (Jlystrix cristata, Sphingurus, Ereihizon 

 dorsatus l ). 



In the Chinchillidae and Dasyproctidae the arrangement is the 

 same (Chinchilla, Lagostomus, Dasyprocta cristata, Ccelogenys). 



In the Caviidae the gluteus maximus has the same bony attach- 

 ment as in Sphingurus (Cavia cobaya, Ceredon rupestris). 



Among the Sciuromorpha the sartorius rises from the outer 

 part of Poupart's ligament and runs to the inner side of the knee, 

 where it blends with the gracilis in Sciurus, Spermophilus, and 

 Pteromys oral. The gluteus maximus is inserted by two slips, one 

 into the third trochanter, the other into the lower part of the 

 femur. It also has, of course, the usual fascial insertion. 



In Xerus the arrangement is the same, except that the gluteus 

 maximus has its bony insertion into the junction of the upper and 

 middle thirds of the femur. 



In Arctomys marmotta this muscle is inserted into the third 

 trochanter and fascia. 



In Castor canadensis no sartorial portion was seen, the gluteus 

 maximus being inserted into a ridge halfway down the femur. 



1 P. Z. S. 1882, p. 271. 



