149 



In the ordinary course of the dissection of the supraclavicular 

 triangle, it was noticed that the Omo-hyoid seemed to possess only an 

 anterior belly. This was attached behind the Clavicle at the outer 

 border of the Sterno-mastoid to a band of fibrous tissue covering the 

 posterior aspect of the bone. On disarticulating the Clavicle at its 

 inner end and pulling it forwards, this fibrous tissue showed an inter- 

 mixture of muscular fibres. This was the more evident at its outer 

 extremity where it was continuous with the Trapezius above and the 

 Subclavius below. The Subclavius muscle was strongly developed, and 

 though some of its fibres were continuous with the retro-clavicular 

 band, by far the greater part of the muscle received insertion 

 normally into the groove on the 

 under aspect of the Clavicle. 



Lying below the Subclavius, 

 and entirely distinct from it, was 

 a narrow muscular belly, which, 

 like the Subclavius, but below it, 

 took origin from the cartilage of 

 the first rib. Running outwards 

 along the lower border of this 

 muscle it was attached laterally 

 to the upper border of the 

 Scapula , immediately behind 

 the Suprascapular notch. These 

 features of the case are figured 

 in the schematic drawing con- 

 structed to illustrate it. 



Unfortunately it was impossible to demonstrate the origin of the 

 nerve supplies to the various muscular slips, these having been injured 

 during the previous dissection. 



The abnormality of the Omo-hyoid is by no means an uncommon 

 one ; it constitutes a definite reversional variation. The fibro-muscular 

 band stretching behind the Clavicle from Sterno-mastoid to Trapezius 

 doubtless represents a remnant of the continuous sheet from which 

 these muscles are derived. The accessory belly below the Subclavius 

 is however less easy to explain. Its lateral attachment coincides 

 exactly with that usual for the posterior belly of the Omo-hyoid (which 

 however is a variable quantity). If it is to be considered as represent- 

 ing this muscle and as being a derivative of a portion of the Rectus 

 sheet, then it is necessary to postulate that a more caudal segment 

 of the sheet than usual has persisted and migrated outwards to the 



