282 ANATOMY IN A NUTSHELL. 



belly nf the Omohyoid, and below by the inferior part of the Sterno-cleido- 

 mastoid. .lust beneath the anterior border of the Sterno-cleido-mastoid is the 

 common carotid sheath which is described in connection with this triangle, 

 although it is under this muscle. This sheath contains the common carotid 

 artery internally, the internal jugular vein externally, and the pneumogastric 

 nerve between the two but on a plane posterior to them. This sheath is bound- 

 ed i\ front by branches from the loop of communication; on the inner side 

 by the trachea, thyroid gland, and the lower part of the larynx; behind by 

 the inferior thyroid artery, re< urrent laryngeal nerve and the sympathetic nerve. 



The second triangle, superior carotid, or triangle of election, is bounded 

 below by the anterior belly of the Omo-hyoid; behind by the Sterno-cleido - 

 mastoid; above by the Digastric. Its roof is made of skin, superficial fascia, 

 Platysma myoides, and deep fascia. Its floor is made of four muscles, Thyro- 

 hyoid. Hyo-glossus, Inferior constrictor, and Middle constrictor. The external 

 carotid artery has eight branches, five of which are in this triangle, viz., superior 

 thyroid, lingual, facial, ascending pharyngeal, and occipital, with their corres- 

 ponding veins, all of which empty into the internal jugular, except the occipital 

 which may empty into the external jugular. 



The third triangle, or digastric, or submaxillary niangle, is bounded in fkont 

 by the anterior belly of the Digastric; behind by the Stylo-hyoid perforated by 

 the posterior belly of the Digastric; and above by the mandible and a line drawn 

 from the angle of the jaw to the mastoid process. Its roof is made of the skin, 

 superficial fascia, Platysma myoides, deep fascia, with the seventh nerve ram- 

 ifying in it. Its Moor is formed by the Mylo-hyoid ami Hyo-glossus. This 

 triangle is divided into two other triangles by the Stylo-maxillary ligament, 

 the anterior one of which contains the submaxillary gland and the posterior 

 one contains the parotid gland. 



The occipital triangle is bounded in front by the Sterno-cleido-mastoid, 

 below by the posterior belly of the Omo-hyoid, and behind by the Trapezius. 

 Its roof is made of the skin, superficial fascia, Platysma myoides, and deep 

 fascia. Its floor from above downward and inward is formed by the Splenius 

 capitis, Levator anguli scapulae, Scalenus posticus and Scalenus medius. The 

 spinal accessory nerve crosses this triangle from the Sterno-cleido-mastoid to 

 the Trapezius. A row of lymphatic nodes lie along the posterior border of the 

 Sterno-cleido-mastoid in this triangle. 



The subclavian or supraclavicular triangle is bounded above by the pos- 

 terior belly of the < )mo-h void. in front by the Sterno-cleido-mastoid, and below 

 by the clavicle. Its roof is made by the skin, superficial fascia, Platysma 

 myoides, and deep fascia and has the suprascapular vessels and nerve lying in 

 it. Its floor is made of the digitations of the Serratus magnus, Scalenus pos- 

 ticus. Scalenus medius, and part of the first rib. It has a few lymphatic glands 

 in it. 



Tiir. Suboccipital Triangle. (Plate CXI.) 



The suboccipital triangle is bounded EXTENALLY by the Superior oblique; 

 below by the Inferior oblique,and internally by the Rectus capitis posticus 

 major. The floor of this triangle is formed by the posterior occipito-atlantal 



