1897.] NRAV YORK ACADEMY OF SCIENCES. 349 



the transition stage from the regular occurrence in the lower 

 mammalian orders to the absence in the highest Primates. 



5. M. SCALExNUS. 



(PI. XXVIII. and XXXIY.) 



The Scalenus group lies entirely dorsad of the axillarj^ ves- 

 sels and brachial plexus, as these structures cross the first rib. 



The ventral portion of the muscle {Scalenus anticus) is small, 

 inserted into the ventral margin of the first rib, just cephalad of 

 the attachment of the lateral portion of the Supracostal muscle. 



The remainder of the muscle (Scalenus medius and posticus) 

 descends over the lateral surface of the thorax in two bundles, 

 a mesal and a lateral. The former is inserted into the cephalic 

 border and ectal surface of the fifth rib, having passed beneath 

 the cephalic digitation of the External Oblique muscle, just 

 mesad of the origin of the Serratus anterior from the fifth rib 

 (PI. XXVIII. and XXXIV.) The lateral division of the Scale- 

 nus passes beneath the fourth digitation of the Serratus to be in- 

 serted into the cephalic margin and ectal surface of the fourth 

 rib (PI. XXVIII. and XXXIV). The thoracic extension of the 

 Scaleni, and the situation of the muscles dorsad of the vessels 

 and nerves of the forelimb in their passage over the first rib, ap- 

 pear to be characteristic throughout the Lemuroidea. 



Murie and Mivart (1, p. 22) describe the muscle in Lemur 

 catta as consisting of two masses, " the posterior (dorsal) of 

 which is perforated by the External Thoracic (' Respiratory ') 

 nerve." The}^ describe the anterior (ventral) of these divisions 

 as extending further caudad, being inserted into the second and 

 third ribs (according to Meckel also into the fourth rib), in con- 

 tact with part of the Serratus anterior. They find the same ar- 

 rangement in L. varius, only in this animal the long anterior 

 (ventral) portion descends as far as the fourth rib. 



The same authors describe three or four Scaleni in Lemur 

 xanthomysfax (1, p. 22) as follows : " The longest slip springs 

 from the fourth rib close to the cartilage ; it proceeds forwards 

 (upwards) and about the posterior (lower) third of the neck is 

 joined by another slip which comes from the second and third 

 ribs, in proximity and partial union with the Serratus magnus. 



These two portions of Scaleni are inserted by two tendons 

 into the transverse processes of the second and fourth cervical 

 vertebra. A third portion of the Scaleni comes from the ante- 

 rior (upper) border of the first rib, and is inserted by two ten- 

 dons into the transverse processes of the sixth and fifth cervical 

 vertebrae. All these portions are placed outside the brachial 

 plexus ' 



