1894.] MYOLOGY OF RODENTS. 287 



the upper third to half of the linea aspera of the femur. The 

 only exceptions to this that I have met with are the Caviidae, in 

 which the muscle rises by a tendon from the ilio-pectineal eminence 

 only (Cavia cobaya, Ceredon rupestris), and Castor, in which it is 

 very strongly developed and is inserted into the whole length of 

 the shaft of the femur. 



Quadriceps Extemor Cruris. — The four muscles composing the 

 quadriceps have the same origin and insertion that they have 

 in Man, and are practically the same in all the Hystricomorpha 

 and Sciuromorpha. The rectus rises by two heads, which are some- 

 times quite distinct, but at others so short as to be almost indis- 

 tinguishable. They are perhaps most distinct in the Hystricidae, 

 least so in the Sciuridae. The crureus rises from the wdiole of 

 the anterior surface of the femur by a series of about 30 fleshy 

 arches. The two vasti can usually be separated easily from the 

 crureus ; as a rule the vastus externus is the larger. 



Adductors. — It is extremely difficult in dissecting a Rodent to 

 say which part of the adductor mass corresponds to the adductor 

 longus, brevis, or rnaguus of human anatomy. 



In Dipus cer/i/ptius the adductor longus rises from the front of 

 the pubes under cover of the gracilis and runs to the inner side of 

 the patella. The adductor magnus and brevis come from the whole 

 subpubic arch and are inserted into the upper two-thirds of the 

 back of the femur. A good deal of the adductor mass, however, in 

 this animal seems to be blended with the semimembranosus. 



In the Octodontidae and Chinchillidae the adductors longus 

 and brevis seem to be fused, although in Aulacodus and Octodon a 

 division was readily made out. These coalesced muscles rise from 

 the inner part of the pectineal line and ventral surface of the 

 symphysis, and are inserted into the upper half of the linea aspera. 



In the Hystricidae, as Meckel 1 observes, the three parts of the 

 muscle can be seen ; this is especially the case in Sphingurus, but it 

 is doubtful whether the three parts correspond morphologically with 

 the three adductors in Man. 



Among the Dasyproctidae, Dasyprocta has very much the same 

 arrangement as the Chinchillidae, but in Coelogenys paca the adductor 

 brevis has a distinct insertion by a ribbon-like tendon into the 

 upper part of the liuea aspera. 



It will be noticed that nothing has been said here about fibres 

 passing to just above the internal condyle ; these have already been 

 described with the semimembranosus. 



Among the Sciuromorpha the adductor mass is much more broken 

 up. 



. In Sciurus, wdiich serves as a good type, there are five portions 

 inclusive of the slip already described with the semimembranosus. 

 The following is the arrangement in Sciurus: — (1) Most anterior 

 portion from the ilio-pectineal line to the middle of the posterior 

 border of the femur ; this part is distinct from the pectineus. 

 (2) A slip from the posterior part of the pubic symphysis to above 

 1 Traite general d'Anatomie comparee, vol. yi. p. 378. 



