262 THE VASCULAR SYSTEM. 



internally and above by the J/. coccygeo-iliacuit, below and exter- 

 nally by the origin of the M. vast us externus, and below by the 

 M. pyramidalis. Each posterior heart is about two lines long- and 

 one broad, with its long axis placed antero-posteriorly ; the outer 

 surface is uneven and appears to be unequally dilated. The lymph- 

 heart is closely attached to the surrounding parts, especially to 

 the fascia covering the M. ilii-coccyyea, and posteriorly to the 

 M. levator ?and the M. pyramidalis. [The posterior lymph-hearts 

 receive lymph from the parts surrounding them, and from the 

 hinder extremities, and forward it into the V. iliaca cotitmnnicans. 



The posterior lymph-hearts are each supplied by a branch from 

 the corresponding coccygeal nerve (Waldeyer) by its dorsal branch. 

 The lymph-hearts are also in close connection with the sympathetic 

 system (Waldeyer).] 



PART III, 



THE BLOOD, LYMPH, AND HISTOLOGY OF 



THE VESSELS, 



[The parts described in this section will be considered very 

 briefly, and only from an anatomical point of view. 



A. The blood : . 



The blood varies in colour, according as it is obtained from an 

 artery or from a vein ; from an artery it has a bright red or scarlet 

 colour ; from a vein a darker shade : in the pulmonary vessels these 

 colours are reversed. The blood consists of a fluid plasma which 

 contains red and white corpuscles : the whole forming a slightly 

 alkaline, opaque, and somewhat sticky fluid. 



a. The plasma or liquor sanguinis is a transparent, clear, slightly 

 yellow fluid, faintly alkaline in reaction. 



1 Mr. Hurst has noticed a frog (K. temporaria) in which the blood was perfectly 

 colourless. 



