DISSE CLION. OF THE NECK. 63 
tertius; it arises from the transverse process of the 
7th cervical vertebra. 
4. The Intercostal Muscles. Jtemove the above- 
named muscles and fat, etc., from the thorax; the in- 
tercostal muscles lying between the ribs will be ex- 
posed. 
a. THE EXTERNAL INTERCOSTALS form the external 
layer passing from the posterior margin of one bony 
rib to the anterior margin of the succeeding one; the 
fibres have an inclination inward and to the posterior. 
This layer ceases at the cartilaginous ribs. The layer 
of muscle between these portions of the ribs forms 
the 72Zercartilaginous muscles, and their fibres have an 
inclination in the opposite direction. 
b. THE INTERNAL INTERCOSTALS. Diyissect off the 
external intercostals between two or three of the ribs, 
and the internal intercostals will be exposed; these 
also pass from one bony rib to the other, but have an 
inclination outward and to the posterior. 
DISSECTION OF THE NECK: 
Make an wtnceston along the mrd-line.of the neck 
throuch the skin, and the necessary transverse imets- 
zons at the shoulder. Lay back the flaps of skin on 
both sides. 
1. The Platysma Myoides is a skin-muscle found 
in the neck which may have been reflected with the 
skin. The chief bundle of fibres in it arises from the 
dorsal wall of the anterior portion of the thorax, and 
comes obliquely around to the ventral surface of the 
neck, and continues forward to the head. Scattered 
muscular fibres pass transversely from this during its 
course toward the ventral mid-line of the neck. The 
muscle is attached only to the skin. 
