390 
Avgas persicus 
discs which runs forwards on the dorsal surface towards the anterior 
margin of the body, from a point slightly anterior and external to the 
pair of large discs from which the depressor muscles originate. It may 
be remarked in passing that this series of discs is the representative of 
the cervical grooves of the Ixodid ticks. The lower terminations of the 
levator muscles of the capitulum are inserted into the upper part of the 
postero-lateral angles of the basis capituli. The action of these two 
pairs of capitular muscles is sufficiently explained by their respective 
names. 
The muscles of the chelicerae are three in number, a retractor muscle, 
and the flexor and extensor muscles of the digit. The retractor muscles 
( m.r.ch .) each consist of a stout bundle of fibres which takes its orio-in 
from a large aggregation of small discs occupying the middle of the 
dorsum, immediately posterior to the discs of the depressor capituli 
muscles. The retractor muscles are inserted into the posterior ex¬ 
tremities of the shafts of the chelicerae, along the line where the latter 
are reflected forwards to form the thin membranous inner cheliceral 
sheaths. The flexor and the extensor muscles of the digit are contained 
wholly within the expanded basal portion of the cheliceral shafts (see 
Part I, pp. 37-38). The extensor muscle of the digit is a bipinnate 
muscle, the strands of which are attached, serially, to the inner surface 
of the wall of the expanded basal portion of the cheliceral shaft; the 
latter run forwards and unite to form a central tendon which becomes 
free of the muscle before passing through the narrow cylindrical portion 
of the cheliceral shaft, and is finally inserted into the lateral extremity 
of the expanded base of the digit. The extensor muscle of the digit, 
though smaller than the flexor muscle, resembles it in structure. Its 
tendon is attached to the mesial side of the base of the digit. 
The muscles of the palp consist of a pair, a flexor and an extensor, 
related to each article. The muscles of the basal article take their origin 
from the lateral wall of the basis capituli (see Text-fig. 4). The 
adductor (or extensor) muscle runs forwards and inwards, and is in¬ 
serted into the inner part of the proximal margin of the first or basal 
article. The abductor (or flexor) muscle, which takes its origin from a 
position on the lateral wall of the basis capituli slightly anterior to 
the adductor muscle, runs almost directly forwards, and is attached 
to the lateral part of the proximal margin of the basal article. The 
contraction of the abductor muscle deflects the entire palp in a lateral 
direction, while the adductor muscle by its action in the opposite 
direction restores the palp to its normal position. The remaining 
