1894,] MYOLOGY OP EODElfTS. 283 



Gluteus Medius. — The gluteus uiedius rises from the fascia over 

 the posterior part of the erector spinae, and its continuation into 

 the tail-muscles, from the crest of the ilium and the inferior 

 border of that bone for some distance. It is usually a very large 

 muscle. It is inserted into the outer side of the great trochanter 

 by a number of tendinous slips placed close together. 



This description applies to all the animals dissected, except the 

 Octodontidse, in which there is no origin from the ilium {Myopo- 

 tamus, Capromys, Aulacodus). 



Gluteus Minimus. — This muscle rises from the external surface of 

 the ilium, below the great sciatic notch, and is inserted into the top 

 and front of the great trochanter. It is usually small and very 

 difficult to clearly separate from the gluteus medius, scausorius, 

 and pyriformis. In Aulacodus it is a large muscle folded on 

 itself, rising from the fascia over the tail-muscles as far forwards 

 as the crest of the ilium, then from the outer side of the ihum as 

 far back as the acetabulum ; it thus springs from a horseshoe- 

 shaped origin above, below, and in front of tlie sacro-sciatic notch, 

 which it encloses in the concavity of the horseshoe. Capromys 

 presents a somewhat similar arrangement, but in the other animals 

 examined there was no variation of any importance from the 

 normal. 



Scansorius. — The scansorius may be present as a distinct muscle, 

 or may be so blended with the gluteus minimus as to make it 

 impossible to distinguish it. When it is distinct it rises from the 

 inferior border of the ilium, and is inserted into the anterior 

 surface of the great trochanter. 



In the Dipodidae it is present as a distinct muscle (Dipus 

 (egyp>tius). 



In the Octodontidae it is probably represented by the inferior 

 portion of the gluteus minimus ; in Myopotamus it is more distinct 

 than in Capromys or Aidacodus. 



In the Hystricidae nothing was seen of it in Hystrix or Sphin- 

 gurus; in Erethizon dorsatus it is absent according to Mivart \ but 

 in E. epia-antlms it is well marked according to "Windle ^. 



In the Chinchillidae I made it out in Viscacha, but failed to in 

 Chinchilla. 



In the Dasyproctid^ it is present both in Dasyprocta and 

 Ccelogenys, but is much more distinct in the former. 



In the Caviidffi it is present, and is inserted into a tubercle on 

 the outer side of the great trochanter at its junction with the 

 shaft {Cavia cobaya, Ceredon ruijestris). 



It was absent in all the S'ciuromorpha examined (Sciurus, 

 Pteromys, Xerus, Spermophilus, Arctomys, Castor). 



Pyriformis. — The pyriformis rises from the ventral surface of 

 the sacrum close to the sciatic notch, through which its fibres pass, 

 and from the outer surface of the ilium in front of the notch ; by 

 the latter part of its origin it is often fused with the gluteus 

 minimus. It is inserted into the top of the great trochanter. 

 ^ P. Z. S. 1882, p. 271. ^ Journ. Anat. vol. xxii. p. 126. 



