24 FIELD MUSEUM OF NATURAL HISTORY ZOOLOGY, VOL. XIV. 



MUSCLES OF THE BACK. 



Spino-trapezius. Origin from the spines of the thoracic vertebrae 

 from the fifth to the twelfth. Insertion on the middle of the vertebral 

 third of the scapular spine. A thin rather elongate muscle passing for- 

 ward superficial to the dorso-cephalic part of the latissimus dorsi. 

 Dorsally it is separated from the acromio-trapezius by a small fascia 

 overlying the rhomboideus. A separation has been noted also in Nota- 

 ry ctes (Wilson, 1894, p. 6). It is the usual condition in the monotremes, 

 insectivores and certain edentates. In Didelphis, the single muscle is 

 weaker over the shoulder than elsewhere and in Sarcophilus (Macalister) 

 also there is a tendency toward division. In Petrogale, Parsons (1896) 

 found that it had a "continuous fleshy origin except opposite the first 

 thoracic spine, where it is aponeurotic." 



Acromio-trapezius. Origin from the occipital crest slightly laterad 

 of the median line and thence along the nuchal crest to the vicinity of 

 the fifth thoracic spine. Insertion on the front of the scapular spine 

 and metacromion and thence along a fascia crossing the acromio- 

 deltoid to the clavicle. A broad thin sheet covering the dorso-caudal 

 half of the side of the neck and part of the shoulder. 



Latissimus dorsi. Origin from the vicinity of the fifth thoracic 

 spine along the vertebral column to the middle of the third lumbar 

 vertebra and to the lumbar fascia. Insertion in common with that of the 

 teres major entad of the biceps on the side of the bicipital groove. On 

 its lower side near its insertion is the usual connection of the epitro- 

 chlearis. It is more definitely connected to the teres at its insertion than 

 in Didelphis. It has no costal slips and in this agrees with Didelphis, 

 Dasyurus, Notoryctes, Phascolarctos, etc. 



Rhomboideus. This is divisible into Rhomboideus major (vertebralis) 

 and R. minor (capitis). R. major has its origin on the nuchal crest from 

 the occiput slightly caudad of the anterior border of the trapezius to the 

 fifth thoracic spine. Its insertion is on the inner side of the vertebral 

 border of the scapula cephalad of the insertion of the serratus magnus. 

 R. minor has its origin fleshy from the junction of the mastoid, squa- 

 mosal and supraoccipital bones and thence along the occipital crest a 

 distance of about four millimeters. It is a thin flat ribbon free from the 

 vertebral division until a point halfway between the occiput and the 

 scapula where it unites with its fellow. Its insertion is on the anterior 

 distal base of the scapular spine dorsad of the insertion of the "atlanto- 

 scapularis." The rhomboideus in marsupials is usually undivided. 



Levator scapulae. Origin from the transverse processes of the last 

 five cervical vertebrae just entad of the scalenus. Anteriorly a single slip 



