o/'Bradypus tridactylus. 65 



perly that it coexists with the dorsi-epitrochlear muscle, and 

 thus can scarcely be, as Mr. Wood suggests, an imperfectly 

 developed slip of the dorsi-e])itrochlear muscle. Tliis muscle 

 I found in Cfehnfi capueinus (Proc.Nat. Hist, Soc. Dublin, April 

 1866) passing from the cartilages of the eightli, ninth, and 

 tenth ribs to the capsular ligament of tlic shoulder-joint. A 

 similar muscle was described by Mr. Mivart in Cercopithecus 

 sahmus (Proc. Zool. Soc. 1865, p. 44). I liave likewise seen 

 it in Macacus neyiiestntms and sinicus. This muscle is de- 

 scribed and figured by Mr. Wood as an anomaly in human 

 anatomy (Proc. Koyal Soc. 1866, p. 231, and tig. 1) ; it is de- 

 scribed by Zenker in Amphibian reptiles as brachio-abdomi- 

 nalis (Batrachomyologia, p. 39), and by Duvernoy as chondro- 

 epitrochlear in many animals. Prof. Huxley has also given to 

 it the name of costo-humeral. I have found it present in the 

 Seal, Opossum, F//aJaii(/ista, AIacroj)us (/u/anteus, Wallaby, 

 Otter, and as an anoinuly in nuan. Dug^s applies to it the 

 name abdomino-humeralis, and Klein humero-abdominalis. 

 It is strongly nuirked in the Frog, Fipa ainericana and Bvfo 

 cinerea^ and in Lacerta viridis (closely connected to the great 

 pectoral) ; but it does not seem to exist in Ljuana tuhercidata, 

 and is not mentioned in Mr. Mivart's careful description of this 

 species. Its affinities seem certainly to be pectoral, and it 

 seems to be an additional posterior member of that group of 

 muscles ; and its rudiment, I think, is the human '' Achsel- 

 bogen " of Langcr, as supposed by Mr. Clalton. 



Tlie rectus thoracicus lateralis arose from the third, fourth, 

 and fifth ribs, and was inserted into the first rib ; it lay super- 

 ficial to the serratus magims. This was the only thoracic 

 rectus present, as there was no superficial sternalis brutorum 

 or rectus sternalis, nor was the rectus abdominis continuous 

 with it. It was quite separate from, but internal to, the sca- 

 leni muscles. A muscle corresponding to this was described 

 as an anomaly in human anatomy by Mr. Wood and myself 

 some time ago, and I have since met with several instances of 

 it in the dissecting-room ; and a similar muscle I also found 

 m Macacus sinicus and neinesfriiius^ and very distinct in a fine 

 Bengal tiger ; but in them the rectus abdominis was continuous 

 with the muscle, which is not the case in Braih/pus. The in- 

 sertion of this nniscle was a little external to the origin of the 

 subclavius ; and in this respect it corresponded closely to the 

 arrangement in Orijctero-pus capensis^ in which the subclavius 

 origin almost touches the prolonged rectus abdominis — a con- 

 dition described by Meckel and Galton. We can tlius deter- 

 mine the homologies of this lateral rectus, and find it to be 

 nothing but a ])rolonged or detached sli]) of the rectus abdo- 

 minis, displaced outwards or lateralized from its origin. 



