244 Transactio7is of the Boyal Society of South Africa. 
these lateral prolongations as the slits, SI, and the small cup-shaped 
glands Gl, associated with them. 
The second gill-slit or hyo-branchial is shown in Fig. 3 as Sp between 
the hyoid bar (Hy) and the first branchial bar (Br) ; it does not open to 
the exterior. It has no gland associated with it. 
Fig 2. — 1 backward continuation of anterior choroid plexus; D diencephalon ; 
PB pituitary body ; Gl ganglionar root of nerves 4-7 ; 2 internal jugular vein ; 3 in- 
ternal carotid artery; Th. thymus; M muscle joining 1st branchial bar to cranium 
(see opposite side of section) ; S see text ; 4 systemic arch (3rd last) ; 5 2nd last aortic 
arch ; 6 last aortic arch (pulmo-cutaneous) ; Ly lymph spaces ; CA conus arteriosus ; 
Th2 thymus. 
The three branchial slits begin in the floor of the pharynx as grooves 
running obliquely backwards and opening through slits the anterior ends 
