270 SHOULDER-GIRDLE IN MONOTREMES, 



of the two ; it then has insertion on the distal part of the pectoro- 

 deltoid ridge. 



Special Regions and Muscles. 



The Hyo-dermal slip. — As the superficial layer of the panniculus 

 runs over the ventral aspect of the cervical region, there is 

 developed a well marked band of muscle on either side from its 

 deep (dorsal) surface. These bands run forward and inwards, and 

 piercing the fascia of this region, are inserted in the basi-hyoid 

 close to the median line. 



M. dermo-dorsi cervicalis (Fig. 12, D. D. C). — This muscle 

 arises from the 11th, 12th, and 13th ribs; the inner margin of 

 the slip from the 11th rib being placed about 1-5 cm. from the 

 mid-line, while the more posterior slips are placed further out (the 

 opposite condition holding in Echidna). These slips run forward 

 and outwards, and coalescing, form a fiat band of muscle which 

 lies on the postero-external margin of the trapezius. Running 

 forward the band becomes narrow, and passing over the insertions 

 of both divisions of the trapezius on the scapula, the inner fibros 

 of the muscle now become connected with an aponeurosis which 

 stretches over the mid-dorsal line to the fellow muscle on the 

 opposite side ; while the terminal fibres are lost in the orbital 

 regions. 



The dermo-brachio-cephalic bands arise in two parts as in 

 Echidna. The dorsal band has origin from the well marked 

 depression on the parietal bone, immediately anterior to the origin 

 of the trapezius. The ventral part arises from the superior maxilla 

 and processus alveolaris, and ventrally by an aponeurosis which 

 stretches over the inter-mandibular muscles. The ventral divisions 

 run backwards over the buccal pouch, and after being joined by a 

 slip attached to the hyoid bone, coalesce with the dorsal portion 

 forming a figure like the letter Y; the auricle being placed in the 

 fork of the Y. The united muscles are now continued as a long 

 thin band to be inserted on the distal third of the external border 

 of the ulna ; being placed as in Uchidna beneath the derrao-flexor 

 antebrachii. 



