146 DISSECTION OF THE DOG 



Mm. levatores costabum. — The levators of the ribs are a series of small 

 muscles arising from the transverse processes of the thoracic vertebrae. The 

 fibres of each muscle run in a caudal and ventral direction to be inserted into 

 the cranial border of the rib succeeding the vertebra from which they have taken 

 origin. 



Dissection. — The muscles of the tail should now be cleaned and examined. 



Mm. sacro-coccygeus dorsales. — The dorsal sacro-coccygeal muscles are 

 two in number, a medial and a lateral. The medial muscle arises from the 

 spinous processes of the lumbar, sacral, and first coccygeal vertebrae, and is 

 inserted into the dorsal surface of the coccygeal vertebrae. 



The lateral muscle springs from the articular processes of the last three 

 lumbar and all the sacral vertebrae, and from the transverse process of the first 

 coccygeal vertebra. Rounded tendons pass over several vertebrae and are 

 inserted into the dorsal aspect of all the bones of the tail. 



M. sacro-coccygetts ACCESSORius. — The accessory sacro-coccygeal muscle 

 may possibly represent the intertransverse muscles of other regions. It is 

 a rounded muscle lateral in position to the preceding and with origin from the 

 dorsal border of the ilium, the lateral border of the sacrum, and the transverse 

 process of the first coccygeal vertebra. The insertion is into the side of the 

 tail vertebrae. 



M. coccygetjs. — The coccygeal muscle has already been examined. 



Mm. sacro-coccygeus ventrales. — As on the dorsal, so on the ventral 

 side of the tail, there are medial and lateral muscles. 



The lateral ventral sacro-coccygeal muscle arises from the ventral face of 

 the last lumbar vertebra, the sacrum, and the transverse processes of coccygeal 

 vertebrae. By long tendons the muscle is inserted into the ventral surface 

 of the bones of the tail. 



The medial muscle springs from the ventral surface of the sacrum and the 

 first coccygeal vertebra, and is inserted into the corresponding aspect of the tail 

 vertebrae. 



Dissection.— Reflect the skin from the ventral side of the neck and the 

 mandibular region. Secure the previously detached manubrium of the 

 sternum and the first costal cartilage, so as to keep the ventral cervical 

 muscles on the stretch. Then clean up the external jugular vein on the 

 side from which the limb has been removed. 



V. jugularis externa.— The external jugular, much larger than the 

 internal vessel of the same name, is the main vein of the neck. Formed at the 

 aboral border of the submaxillary gland by the union of the external and internal 



