42 



PHLEBOTOMY INSTRUMENTS. 



as regards height, etc., and while blood-pressure within it is low, a 

 considerable volume of blood may be obtained in a short time. It 

 lies in the " jugular furrow," formed above by the mastoido-humeralis 

 and below by the sterno-maxillaris muscles. Beneath the skin and 

 loose connective tissue lies the panniculus, which, though very thin 

 in the upper portion of the neck, attains half an inch in thickness 

 in the lower. In the upper half of the jugular furrow " the vein 

 rests on the subscapulo-hyoideus muscle, which there separates the 

 vessel from the carotid artery ; but in the lower half the vein rests 

 on the side of the trachea, and is in direct contact with the carotid, 

 which lies above and. slightly internal to it." The point chosen 

 is the junction between the upper and middle thirds of the neck, 



Fig. 196. — Lancets for venesection. 



where the subscapulo-hyoideus muscle intervenes between the vein 

 and the carotid artery, which is therefore less likely to be injured. 



The average quantity of blood abstracted at one time is, in the 

 ox, 10 to 16 pints, the horse 8 to 12 pints, the pig 1 to 1| pints, sheep 

 f of a pint, and dog \ a pint, in fowls 2^ to 10 fluid drachms ; 

 individual peculiarities, however, must be taken into account in 

 each case. 



Instruments. The simplest instrument is the lancet. Several 

 forms are used, the varieties of which are shown in Fig. 196. The 

 English lancet (a) has a relatively obtuse point ; the German (b) is 

 somewhat more acute ; in the Italian (c) the blade is narrower from 

 the commencement, and the cutting edge relatively long and slender ; 

 d is the sabre-shaped or abscess lancet, having one convex, and one 

 concave cutting edge. 



To bleed with the lancet, though apparently easy, requires con- 



