632 Proceedings of the Royal Irish Academy. 



abductor caiidm anterior of the canine tribe (W. Krause), presents 

 great rarieties in the degrees of its deyelopment. Three times I have 

 found complete absence of the muscular fibres ; in one of these the 

 deficiency was bilateral, and tendinous fibres took the direction of the 

 normal muscular bundles. 



Sacro-coecygeus posticus ; extensor coccygis ; levator coccygis (Mor- 

 gagni). — This bundle of muscular fibres I have found four times in 

 thirty subjects. Once it was bilateral ; once the origin was from the 

 posterior inferior iliac spine ; in the other cases it arose from the 

 posterior surface of the third and fourth bones of the sacrum. "W. 

 Krause regards it as the homologue of the extensor caudce lateralis of 

 the dog. 



Sacro-coccygeus anticus ; curvator coccygis (the homologue of the 

 m. flexor caudc^ of the dog, according to W. Krause). — This band of 

 muscular fibres passes from the fourth and fifth bones of the sacrum, 

 along the front of the coccyx, nearly to the tip of the latter. I found 

 muscular fibres twice in sixteen subjects, and in several others tendi- 

 nous bands occupied the corresponding position. I have also met 

 with these fibres in several other instances, but they were always very 

 weakly developed. 



Transversus perinaei siiperficialis {s. posterior'). — This muscular 

 band, which was first figured by Tiedemann (1822), is described by 

 Les shaft as an anomalous muscle of comparatively rare occurrence 

 (9 per cent.) Krause has, however, found its occurrence much more 

 frequent, and I have myself found it six times in thirty subjects in 

 which it was searched for. I have also met it casually in many other 

 dissections. It was regarded by Theile (1841) as an aberrant slip of 

 the sphincter ani externus. This muscle lies between the layers of 

 the superficial fascia, passing from opposite the inner margin of the 

 ascending ramus of the ischium, or beneath the tuberosity of this 

 bone, forwards and inwards to the central tendinous point of the 

 perinseum. The muscle more generally known as the t. p. super- 

 ficialis has been named by Lesshaft the — 



Transversus perinm medius. — This muscle lies between the deep 

 layer of the superficial fascia (so-called fascia of Colles) and the 

 anterior layer of the triangular ligament. According to Lesshaft, 

 this muscle is absent in thirty-five per cerwt. of the cases examined. 

 In thirty subjects specially examined by me the muscle was eight 

 times absent, the deficiency being bilateral in five cases. In the 

 others the degrees of development varied greatly. 



Transversus perincei profundus (s. anterior'). {Guthrie's muscle; 

 iscMo-bulbosus). — This muscle is placed farther forwards than that 

 already named, and is separated from the anterior margin of the 

 levator ani by the deep layer of the triangular ligament. The degree 

 of development varies greatly, and it was completely absent three 

 times in thirty bodies. 



Gluteo-perinealis (Krause). — This band of muscular fibres, passing 

 from the fascia over the inner margin of the gluteus maximus (oppo- 



