954 THE OSTEOLOGY AND MYOLOGY OF THE DEATH ADDER, 



muscular bundles replace the fascia that overlay the dorsal muscles. 

 This layer is attached to the aponeurosis formed by the tendons of 

 the spinalis dorsi, and it is also prolonged over the head muscles 

 and beneath the mandible. The most anterior of the fasciculi of 

 the deep layer are attached to the quadrate. We thus have formed 

 what is called by Humphry a "superficial brachio-cephalic stratum," 

 which is divided again into a cervicalis superficialis superior and 

 inferior. 



The cervicalis superficialis superior has in turn a superficial 

 portion, constituted by a platysma, and a retractor oris, depressor 

 mandibulse, and retractor quadrati. 



The cervicalis superficialis inferior is represented by an inter- 

 mandibularis anteriorly, and a mylohyoid posteriorly. The deep 

 layer of the external oblique that we saw attached to the quadrate, 

 represents the sterno-mastoid ; while the whole of the cervicalis 

 superficialis superior represents the sphincter colli of birds. 



Platysma. 



M. atlanto-epistro2)heo-hyoideus, Hoffmann ; Rilckwartszieher 

 des Zunc/enbeins, D' Alton. 



The platysma is represented by a slight layer of muscular fibres 

 extending upwards over the retractor oris, and running forward to 

 be lost on the masseter. 



The platysma is not mentioned as occurring in Ophidians ; but 

 the following facts tend to show that we are justified in considering 

 that a platysma is really present. 



In Python hivittatus, D' Alton found a band of muscular fibres 

 extending from the neural spines round to the hyoid bone. We 

 have found the same in Morelia and in Hydrosaurus ; in the 

 latter this band being but a superficial part of the well-developed 

 platysma. 



We see, therefore, the disappearance of a sheet of muscle as a 

 whole from a class of animals in which it could obviously be of no 

 use, but at the same time a specialised band of muscle remains, 

 since it performs a function quite foreign to that of the platysma. 



